The invention relates to a dynamic pressure bearing which performs supporting in the axial direction by means of a flange formed on a shaft.
FIG. 4 shows such a type of dynamic pressure bearing of the conventional art. In the dynamic pressure bearing, dynamic pressure generating grooves 103 and 105 for thrust supporting are formed in both axial end portions of a flange 102 formed on an end of a shaft 101. The flange 102 has through holes 107 and 109 which are adjacent to a portion 106 where the flange is joined to the shaft 101, and which are formed, so as to pass through the flange in the axial direction. Dynamic pressure generating grooves 111 and 112 for radial supporting are formed in the shaft 101.
The shaft 101 and the flange 102 are accommodated in a housing 115 which is configured by a cylinder 108 and a lid 110. The dynamic pressure generating grooves 103 and 105 formed in the flange 102 are opposed to a bearing surface 110A of the lid 110 and a bearing surface 108A of the cylinder 108 with forming a predetermined space therebetween, respectively.
In the dynamic pressure bearing, in the case where a lubricant fluid unbalancedly exists on an upper side or a lower side of the flange 102 during the rotation, the lubricant fluid is caused to flow from the upper side to the lower side or from the lower side to the upper side of the flange 102 through the through holes 107 and 109, so as to eliminate the vertically unbalanced condition of the flange 102.
However, the dynamic pressure bearing of the conventional art involves the following problems. The through holes 107 and 109 formed in the flange 102 reduces an area for forming the dynamic pressure generating grooves 103 and 105. In order to generate a predetermined dynamic pressure, therefore, it is necessary to increase the diameter of the flange. Thus, the outer diameter is disadvantageously increased, and a high torque is required for rotating the shaft.
Therefore, it is an object of the invention to provide a dynamic pressure bearing which can eliminate an unbalanced existence of a lubricant fluid without increasing the diameter of a flange, and which is compact in size and requires a lower rotation torque.
In order to attain the object, the dynamic pressure bearing of the invention of claim 1 is a dynamic pressure bearing having dynamic pressure generating grooves which are formed in an axial end face of a flange formed on a shaft or in a bearing surface opposed to the end face, and characterized in that
the shaft includes: a smaller diameter portion which extends in an axial direction from the axial end face of the flange by a predetermined dimension; and a larger diameter portion which extends in the axial direction from the smaller diameter portion, and
a through hole which passes through the flange in the axial direction is formed, the through hole being adjacent to the smaller diameter portion of the shaft, at least a part of the through hole being opposed to an end face of the larger diameter portion.
In the dynamic pressure bearing according the invention, the axial through hole of the flange is formed so as to be adjacent to the smaller diameter portion of the shaft, and opposed to the end face of the larger diameter portion. That: is, the axial through hole is formed in a region which is further in than the bearing surface of the flange, and hence the axial through hole does not reduce the area of the bearing surface of the flange. According to the invention, therefore, the unbalanced existence of a lubricant fluid can be eliminated by the axial through hole without increasing the diameter of the flange. Accordingly, a stable supporting ability can be exerted, and a compact size and a low rotation torque can be realized.